Charged particle beam irradiation apparatus and irradiation method using the apparatus

ABSTRACT

A charged particle beam irradiation apparatus includes a specimen stage for holding a specimen; a specimen stage drive unit for moving the specimen stage; a detector for detecting the amount of displacement of the moved specimen stage; a charged particle beam optical unit for irradiating the specimen with a charged particle beam; an image display unit for displaying an image of the specimen, the image being formed by using charged particles or electromagnetic waves emitted from the specimen irradiated with the charged particle beam; a marker display unit for displaying a marker on each target position on an image of the specimen, on a viewscreen of the image display unit; a marker position input unit for designating reference positions on the image of the specimen; and a marker position calculation unit for calculating the position on which each marker is displayed on the image of the specimen on the viewscreen of the image display unit; wherein the position on the image of the specimen, on which each marker is to be displayed, is also moved based on both the calculated position of each marker, which has been calculated by the position calculation unit, and the amount of displacement of the moved specimen stage, the amount of displacement being detected by the detector.

[0001] This is a continuation of application number 09/264,465 filedMar. 9, 1999.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a charged particle beamirradiation apparatus such as a scanning electron microscope, an X-raymicro-analyzer, and so on, and an irradiation method using theirradiation apparatus, and especially relates to an improved chargedparticle beam irradiation apparatus and an irradiation method using theirradiation apparatus, in which a display unit is used to designate aposition on an image of a target area in a specimen, the target areabeing observed or analyzed by irradiation with a charged particle beam.

[0003] Scanning electron microscope, an X-ray micro-analyzer, etc., areknown charged particle irradiation apparatuses. In a scanning electronmicroscope, a specimen is observed or inspected by using a magnifiedimage of the specimen, which is formed by detecting secondary electronsor reflected electrons generated from the specimen irradiated with anelectron beam. On the other hand, in an X-ray micro-analyzer, a specimenis examined by analyzing an X-ray emitted from the specimen irradiatedwith an electron beam. When a target area in a specimen, to be observedor analyzed by irradiation with a charged particle beam, is designated,a larger view of the specimen is displayed on an image display unit suchas a CRT, an observation monitor, etc., by decreasing the magnificationof the charged particle beam irradiation apparatus, and an image of thedesignated area in the specimen is moved near the central point on aviewscreen of the image display unit. Afterward, by gradually increasingthe magnification, a view with the required magnification is obtained.However, since the magnified size of an inspected region in the specimenis smaller than the image resolution of the image display unit at thelow magnification, the fine structure of the specimen is invisible, andit is difficult to find a point in the specimen to observe. Thus, anoperator searches an inspected point in the displayed view byalternately repeating the specimen movement performed by operating aspecimen fine movement device, and increasing the signification; or bymoving the specimen fine movement device while observing the specimenwith the magnification kept somewhat high.

[0004] Recently, there has been a stronger tendency for the inspectionof a semiconductor memory to be performed with a scanning electronmicroscope in the fabrication processing of semiconductor memories.Usually in a semiconductor memory, a large number of cells with the samestructure are arranged in an orderly latticework. Therefore, it is verydifficult to quickly find a target cell on the viewscreen of a scanningelectron microscope. When an operator searches a target cell in aspecimen such as the above-mentioned semiconductor memory, the operatorneeds to memorize the row and column coordinates of the target cell inthe specimen, and then find the target cell by counting the number ofrows and columns in the latticework pattern by maintaining a somewhathigh magnification such that the operator can discriminate each cell,and by gradually moving the specimen with a specimen fine movementdevice.

[0005] In a new type scanning electron microscope such that disclosed inJapanese Patent Application Laid-Open Hei 4-27908, if an operatordesignates any target position which s/he wants to observe in an imagedisplayed on a viewscreen of an image display unit, a specimen finemovement device is automatically controlled by a motor so that thedesignated position is set at the central position of the viewscreen ofthe image display device. However, the operator needs to find the targetposition on the image of the specimen, which gives a comparatively heavyload on the operator.

[0006] The following method using the above new type scanning electronmicroscope has been devised as a measure to reduce the load of theoperator having to designate a target position on the viewscreen of theimage display unit. That is, in the new type scanning electronmicroscope, the first and second windows for displaying two images ofthe specimen, which are processed with high and low magnificationrespectively, are provided in the image display unit of this scanningelectron microscope. Moreover, an area cursor is also displayed in thefirst window for the image processed with low magnification.Furthermore, it is possible to display the region inside the area cursorin the second window for high magnification. Thus, if the operatorintends to observe a target cell at a position far from a terminal sideposition in a semiconductor memory, from which the searching of thetarget cell is started, the image of the specimen is displayed in thefirst window with a sufficiently decreased magnification, and theposition where the target cell is located is enclosed in the areacursor. Further, the region enclosed in the area cursor is displayed inthe second window with an appropriately increased magnification.

[0007] However, in the above-mentioned conventional scanning electronmicroscopes, if an operator searches for a position apart from one at aterminal side of a specimen by tens of columns or rows in an imageformed with the magnification kept high to a extent such that theoperator can discriminate the structure of a cell to be analyzed, theoperator has to count the number of columns or rows from the terminalside to the position of the target cell. Also, in the scanning electronmicroscope with the ability to display images of the specimen atdifferent magnifications, since an image of the target cell structure tobe analyzed is too small on a viewscreen displaying a low-magnificationimage, it is difficult to count the number of columns or rows of cells.Even if the scanning electron microscope has the ability toautomatically move the designated position of an image of the targetcell in the specimen displayed on the viewscreen to the central positionof the viewscreen, it is still necessary to count cells in the specimenwhile maintaining the magnification as high as necessary. Further, ifthe target cell is at a position far from a terminal side of thespecimen by tens or hundreds of columns or rows of cells, since thetarget cell cannot be found with single specimen-movement operation, itis necessary to repeat the specimen-movement operation to find thetarget cell. The parallel execution of both the counting of the numberof columns or rows and the repeating of the specimen-movement operationis likely to cause an error in the operator's counting of the number ofcolumns or rows, for example, missing some columns or rows.

SUMMARY OF THE INVENTION

[0008] The present invention has been achieved in consideration of theabove mentioned problems. For example, it is effective for solving theproblems of both providing a means to reduce a lord of finding a targetposition in a specimen, and of counting the number of columns or rows inan orderly latticework pattern of cells in the specimen with the samestructure. Thus, an object of the present invention is to provide acharged particle beam irradiation apparatus wherein the searching fortarget cells to be observed in a specimen by operating a viewscreen withimages of cells of the specimen can be easily carried out by an operatoreven if there are many cells arranged in the specimen in an orderlylatticework.

[0009] The above object of the present invention is attained byproviding a charged particle beam irradiation apparatus in which if anoperator attaches a marker to a position to be observed on the image ofa specimen, the marker also is moved along with the position of thespecimen image as though the marker were attached to the position of theactual specimen when the image of the specimen is moved.

[0010] The present invention provides a charged particle beamirradiation apparatus comprising:

[0011] a specimen stage for holding a specimen;

[0012] a specimen stage drive unit for moving the specimen stage, adetector for detecting the amount of displacement of the moved specimenstage;

[0013] a charged particle beam optical unit for irradiating the specimenwith a charged particle beam;

[0014] an image display unit for displaying an image of the specimen,the image being formed by using charged particles or electromagneticwaves emitted from the specimen irradiated with the charged particlebeam;

[0015] a marker display unit for displaying a marker on each targetposition on an image of the specimen, the image being displayed on aviewscreen of the image display unit;

[0016] a marker position input unit for designating reference positionson the image of the specimen, on which respective markers are displayed;and

[0017] a marker position calculation unit for calculating the positionon which each marker is displayed on the image of the specimen on theviewscreen of the image display unit;

[0018] wherein, when the specimen stage is moved, the position on theimage of the specimen on which each marker is to be displayed is alsomoved based on both the calculated position of each marker, which hasbeen calculated by the position calculation unit, and on the amount ofdisplacement of the moved specimen stage, the amount of displacementbeing detected by the detector.

[0019] The present invention further provides a charged particle beamirradiation apparatus comprising:

[0020] a charged particle beam optical unit for irradiating a specimenwith a charged particle beam;

[0021] a charged particle beam deflection unit for moving an area on thespecimen, which is irradiated with a charged particle;

[0022] an image display unit for displaying an image of the specimen,the image being formed by using charged particles or electromagneticwaves emitted from the specimen irradiated with the charged particlebeam;

[0023] a marker display unit for displaying a marker on each targetposition on the image of the specimen, the image being displayed on aviewscreen of the image display unit;

[0024] a marker position input unit for designating reference positionson the image of the specimen, in which respective markers are displayed;and

[0025] a marker position calculation unit for calculating the positionon which each marker is displayed on the image of the specimen on theviewscreen of the image display unit, along with the amount ofdisplacement of the image moved by the charged particle beam deflectionunit;

[0026] wherein, when the image is moved by the charged particle beamdeflection unit, the position on the image of the specimen on which eachmarker is to be displayed is also moved, based on both the calculatedposition of each marker, the position being calculated by the positioncalculation unit, and the amount of displacement of the image, the imagedisplacement being calculated by the position calculation unit.

[0027] Moreover, in accordance with the above charged particle beamirradiation apparatus, the marker display unit displays a marker on theposition on the image of the specimen corresponding to the same positionin the coordinate system for the specimen, even if the image of thespecimen is moved by moving the specimen stage.

[0028] Further, in accordance with the above charged particle beamirradiation apparatus, the marker display unit automatically displaysmarkers by successively changing each of subindices for the markers-each marker being labeled with a subindex including a letter and/or anumeral -on positions where the marker position calculation unitdetermines that markers should be displayed, based on subindices inputfor markers attached to at least two reference positions on the image ofthe specimen, the reference positions being designated from the markerposition input unit.

[0029] Also, in accordance with the above charged particle beamirradiation apparatus, when one of the subindices is selected, themarker display unit moves the image of the specimen so that a markerlabeled with the selected subindex is displayed on the viewscreen of theimage display unit.

[0030] Additionally, in the above charged particle beam irradiationapparatus, the marker display unit displays markers on positions on theimage of the specimen, determined based on the direction and a pitchbetween two neighboring positions calculated by using a first referenceposition and a second reference position on the image of the specimen,the two reference positions being input from the marker position inputunit.

[0031] On top of that, in accordance with the above charged particlebeam irradiation apparatus, the marker display unit displays markers onpositions on the image of the specimen, obtained by dividing theinterval between the first and second reference positions on the imageof the specimen by an input division number, the two reference positionsbeing input from the marker position input unit.

[0032] Furthermore, the present invention provides a method ofirradiating a specimen with a charged particle beam and displaying animage of the specimen, the image being formed by using charged particlesor electromagnetic waves emitted from the specimen irradiated with thecharged particle beam, the method comprising the steps of:

[0033] displaying a marker on each target position on an image of thespecimen, the image being displayed on a viewscreen of the image displayunit;

[0034] reading in and calculating the position of the displayed image onwhich the marker is displayed, in the coordinate system for theviewscreen;

[0035] moving a specimen stage on which the specimen is held

[0036] detecting the amount of displacement of the moved specimen stage;and

[0037] moving the marker to a new position to be located in thecoordinate system for the viewscreen based on both the read-in andcalculated position and the detected amount of displacement of the movedspecimen stage.

[0038] Moreover, the present invention also provides a method ofirradiating a specimen with a charged particle beam and displaying animage of the specimen, the image being formed by using charged particlesor electromagnetic waves emitted from the specimen irradiated with thecharged particle beam, the method comprising the steps of:

[0039] displaying a marker on each target position on an image of thespecimen, the image being displayed on a viewscreen of the image displayunit;

[0040] reading in and calculating the position of the displayed image onwhich the marker is displayed, in the coordinate system for theviewscreen;

[0041] moving an irradiation region of the specimen, which is irradiatedwith a charged particle beam;

[0042] calculating the amount of displacement of the image of thespecimen due to the moving of the irradiation region; and

[0043] moving the marker to a new position to be located in thecoordinate system for the viewscreen based on both the read-in andcalculated position and the calculated amount of displacement of themoved image.

[0044] By the above-mentioned marker display function according to thepresent invention, the marker displayed on the designated position inthe specimen behaves as if the marker were adhered to the specimen. Forexample, in the charged particle beam irradiation apparatus according tothe present invention, if the position on the image of the specimen, onwhich the marker is displayed, moves to the outside of the viewscreen,the marker also moves to the outside of the viewscreen along with theposition on the image of the specimen, and disappears from theviewscreen. Conversely, if the position on the image of the specimen, onwhich the marker is to be displayed, moves into the viewscreen of theimage display unit, the marker also moves into the viewscreen along withthe above position on the image of the specimen, and is displayed on theviewscreen.

[0045] Furthermore, the charged particle beam irradiation apparatus andmethod according to the present invention has an ability to display amarker on each position on the image of the specimen, satisfying thedirection and a pitch which are determined based on the positionalrelationship between designated first and second reference positions towhich markers are attached, respectively, and an ability to display amarker on each of the positions on the image of the specimen, thepositions being obtained by dividing the interval between the first andsecond positions on which markers are displayed, by a divisional numberinput from the input unit, and so on.

[0046] Further still, the charged particle beam irradiation apparatusand method according to the present invention has an ability tosuccessively label each of the target positions to be observed on theimage of the specimen with a subindex composed of a letter and/or anumeral by automatically changing the subindex. If the subindices arenumerals, the markers are automatically labeled with subindices in anincreasing order, such as a series of 1, 2, 3 . . . , or in a decreasingorder, such as a series of 1, 3, 5, 7 . . . . On the other hand, if theyare alphabetic letters, the markers are labeled with letters of a seriesof a, b, c . . . , or a series of z, y, x . . . . If the subindices arealphanumeric pairs, the markers are systematically labeled withsubindices composed of the pairs by automatically changing the numeralsin the subindices in an increasing or decreasing order.

[0047] If the markers are labeled with subindices, it is possible toprovide an additional function for the charged particle irradiationapparatus, such that by inputting a marker with a subindex, an image ofthe specimen with the marker with the designated subindex is moved so asto be displayed on the viewscreen of the image display device.

[0048] The moving of the image of the specimen can be carried out bymoving the specimen stage with the specimen stage drive unit or bymoving an irradiation area of the specimen, which is two-dimensionallyirradiated with a charged particle beam by the charged particle beamdeflection unit.

[0049] Furthermore, the displaying of a marker with a designatedsubindex on the viewscreen of the image display device can be realizedby adding a function to the charged particle beam irradiation apparatus,which calculates the necessary amount of movement of the irradiationarea based on the present position of the marker with the designatedsubindex in the coordinate system for the viewscreen, and if thecalculated amount of the movement of the irradiation position is withinthe range in which the irradiation area can be moved by the beamdeflection unit, it moves the irradiation area by the calculated amountby using the charged particle beam deflection unit. Otherwise, thedisplaying of a marker with a designated subindex on the viewscreen canbe realized by providing an additional function to control the specimenstage drive circuit so as to move the position of the marker with thedesignated subindex by the calculated amount.

[0050] According to the above function for moving the position of animage of a cell to which a designated marker is attached, it is possibleto immediately return back the position of an image of a cell, on whichthe designated marker is to be displayed but which is outside theviewscreen, onto the viewscreen when a subindex in the target marker isinput. Furthermore, markers can be automatically attached to therequired positions on the image of the specimen by designating the firstand second reference positions with two markers, respectively.

[0051] Also, a marker is attached to the position of an image of adesired cell in the specimen and displayed on the viewscreen, by movinga pointer controlled by a pointing device to the desired position andpushing a button switch of the pointer device at the position indicatedby the pointer.

[0052] In accordance with the present invention, once an operatordesignates the position of an image of a cell in a specimen, which theoperator intends to observe, by using a pointing device which controls apointer such as a cross or arrow cursor, and attaching a marker with asubindex of a numeral and/or a letter to a desired position designatedwith the pointer, the attached marker can move along with the positionto which the marker is attached when the specimen is moved. Accordingly,if the position on the image of the specimen to which a marker isattached leaves the viewscreen of the image display device, the markeralso leaves the viewscreen. Conversely, if the position on the image ofthe specimen which has been outside the viewscreen returns to theviewscreen of the image display device, the marker is also displayed onthe viewscreen. Thus, since a desired position on the image of thespecimen can be found by searching or designating a marker attached tothe desired position, and it is not necessary to memorize the position,the locating of the desired position can be efficiently performed by anoperator. Moreover, if an operator designates two or more referencepositions on the image of the specimen by attaching different markers tothe respective reference positions, markers can be automaticallyattached to a plurality of positions on an image of the specimen.Furthermore, each marker can move along with a corresponding one of theplurality of positions to which the markers are attached. Thus, a fieldto be displayed on the viewscreen on the image of the specimen can beefficiently set even though the specimen is a semiconductor memory inwhich a number of unit cells are arranged in an orderly manner. Inaddition, if a subindex of a numeral and/or a letter is included in eachmarker, the efficiency of setting the displayed view field on the imageof the specimen can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053]FIG. 1 is a schematic diagram showing the composition of a chargerparticle beam irradiation apparatus using a scanning electronmicroscope, of an embodiment according to the present invention.

[0054]FIG. 2 is an illustration showing a perspective view of a specimenand an area scanned by the scanning electron microscope.

[0055] FIGS. 3A-7B show examples of displaying an image of a specimen.

[0056]FIG. 8 is a flowchart showing operations of the charged particlebeam irradiation apparatus and processing executed by the irradiationapparatus of the embodiment.

[0057]FIG. 9 is a flow chart showing processing executed by the chargedparticle beam irradiation apparatus of the embodiment when themagnification of the scanning electron microscope is increased.

[0058] FIGS. 10A-15B show examples of displaying markers attached toimages of target cells of a specimen.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0059] Hereafter, details of the embodiments according to the presentinvention will be explained with reference to the drawings. In theembodiments, although a scanning electron microscope is used, thepresent invention can also be used for other types of charged particleanalyzers such as an x-ray micro-analyzer.

[0060] The function of the scanning electron microscope used in thepresent invention is conceptually explained below with reference to FIG.2, and FIGS. 3A and 3B. FIG. 2 is an illustration showing both aperspective view of a specimen 7, for example, a semiconductor memory,in which a large number of unit cells (hereafter, simply referred to ascells) is arranged in a latticework, and an area of the specimen 7,which is two-dimensionally scanned by the scanning electron microscope.The specimen 7 is held on a specimen stage 8 and can be moved by movingthe specimen stage 8. FIGS. 3A and 3B show examples of displaying animage of the specimen 7, which is formed by using secondary electronsgenerated by the scanning of electrons performed by the scanningelectron microscope.

[0061] In the simplest embodiment according to the present invention,which is shown in FIGS. 3A and 3B, when an image of a cell in thespecimen 7 (also referred to as an cell image) comes on the viewscreenof the image display unit, a marker 50 is attached as a sign post to thecell image by using an input means as shown in FIG. 3A. Afterward, ifthe specimen stage 8 is moved in the direction indicated by the arrowshown in FIG. 2, the attached marker 50 is also moved following themovement of the cell in the specimen 7. As a matter of course, it isnecessary to detect the amount of the movement of the specimen stage 8by using a detection means and to estimate the amount of the movement ofthe cell image based on the detected amount of the movement of thespecimen stage 8 and the magnification (M) of the displayed image. Here,expressing the amount of the movement of the specimen stage 8 by thecoordinates (X0, Y0) in the two-dimensional rectangular-coordinatesystem, the displacement amount of the cell image displayed on theviewscreen of the image display unit is expressed by the followingequations (1).

XD=M×X 0

YD=M×X Y 0  (1)

[0062] Therefore, when the specimen stage 8 is moved by X0 and Y0 in theX and Y directions, respectively, by moving the marker 50 attached tothe cell image by the respective quantities of XD and YD in the X and Ydirections, which are calculated by the equations (1), the marker 50 ismoved along with the cell image on the viewscreen of the image displayunit.

[0063] In the examples shown in FIG. 2 and FIGS. 3A and 3B, since the Xand Y directions in which the specimen stage 8 can be moved are the sameas those in the electron beam scanning of the specimen 7, the amount ofthe movement of the marker 50 can be calculated by using the equations(1). However, it actually often occurs that the X and Y directions inwhich the specimen stage 8 can be moved are different from those in theelectron beam scanning of the specimen 7 as shown in FIG. 4. In thiscase, letting the angle between the coordinate system in the movement ofthe specimen stage 8 and that in the electron beam scanning operation berepresented by θ, the displacement amount of the cell image is obtainedby the following equations (2).

[0064] That is, the displacement components XS and YS of the specimenstage 8 in the coordinate system of the two-dimensional electron beamscanning operation are expressed as follows.

XS=X 0 cos θ−Y 0 sin θ

YS=X 0 sin θ+y 0 cos  (2)

[0065] Furthermore, by multiplying XS and YS by the signification M, thedisplacement components XD and YD of the cell image displayed on theviewscreen of the image display unit can be obtained by the followingequations (3). Thus, when the specimen stage 8 is moved by X0 and Y0 inthe X and Y directions, respectively, by moving the marker attached tothe cell image by the respective quantities of XD and YD in the X and Ydirections, which are calculated by the equations (3), the marker 50 ismoved along with the cell image to which the marker 50 was attached, onthe viewscreen of the image display unit.

XD=M×XS

YD=M×YS  (3)

[0066] In the above-explained case, the image of a cell in the specimen7 is moved by moving the specimen stage 8. On the other hand, anelectron beam deflection unit for moving the field of the viewscreen bymoving an area in the specimen 7, irradiated with an electron beam, isusually incorporated into a scanning electron microscope. When the fieldof the viewscreen is changed by the electron beam deflection unit, themarker 50 needs to be moved along with the cell image, following themovement of the cell. A method of changing the field of the viewscreen,which is performed by the electron beam deflection unit, is explainedbelow with reference to FIG. 5.

[0067]FIG. 5 shows an example of a displayed image of the specimen 7,and also illustrates the displacement amount of the displayed image, thedisplacement being performed by the electron beam deflection unit. Inthe following, the displacement amount of the displayed image isexplained by assuming that the X-Y coordinate system of the electronbeam scanning performed by the electron beam deflection unit is the sameas that of the electron beam deflection unit. It is because thecoordinate system is often made equal in both the electron beamdeflection and the electron beam scanning by winding two coils for thesebeam scanning and deflection operations on the same bobbin. Furthermore,it is assumed that the maximum value of a digital value for a controlamount to deflect an electron beam, which is input to the electron beamdeflection unit, is “255”. It is because a D/A converter of 8 bits or 12bits has been currently used in control circuits, and a D/A converter of8 bits is adopted in this embodiment. In the general conversion of a D/Aconverter, if expressing the maximum deflection quantities of anelectron beam in the respective X and Y directions as X_(e-max) andY_(e-max) according to the normalized maximum input value “+1” whichcorresponds to the input digital control amount “255”, the deflectionquantities XSE and YSE according to the digital control values X_(e) andY_(e) input to the D/A converter are obtained by the following equations(4). Here, the respective X_(e) and Y_(e) have a value of 1-255.

XSE=(X _(e) ×x _(e-max))/256

YSE=(Y _(e) ×Y _(e-max))/256  (4)

[0068] By taking into consideration that the direction of the movementof the cell image, displayed on the viewscreen of the image displayunit, is the reverse of that of the deflection of the field scanned withan electron beam, the above quantities XSE and YSE are converted to thequantities XDE and YDE expressing an actual displacement amount of thecell image displayed on the viewscreen as follows.

XDE=−M×XSE

YDE=−M×YSE  (5)

[0069] Accordingly, when the digital control values X_(e) and Y_(e) inthe X and Y directions are input to the electron beam deflection unit,by moving the marker attached to the cell image by the quantities of XDEand YDE which are calculated by the equations (5) in the X and Ydirections, respectively, the marker 50 is moved along with the cellimage on the viewscreen of the image display unit.

[0070] Furthermore, the movement of the marker 50 due to changing of themagnification is explained with reference to FIGS. 6A and 6B. Here,FIGS. 6A and 6B show examples of displaying the image of the specimen 7at two different levels of magnification, and displaying the movement ofthe position of the marker 50 on the image displayed on the viewscreen.

[0071] Now, as indicated in FIG. 6A, at the magnification of MO, themarker 50 is displayed at the position apart from the central point ofthe viewscreen of the image display unit by a distance of X_(MO) andY_(MO). On the other hand, as indicated in FIG. 6B, at the magnificationof Ml, the marker 50 is displayed at the position apart from the centralpoint of the viewscreen of the image display unit by a distance ofX_(M1) and Y_(M1). Thus, the relationship between the positions (X_(M0),Y_(M0)) and (X_(M1),Y_(M1)) is expressed by the following equations (6)

X _(M1)=(M1/M0)×X _(M0)

Y _(M1)=(M1/M0)×X _(M0)  (6)

[0072] Therefore, when the magnification is changed from M0 to M1, bymoving the marker 50 attached to the cell image according to theequations (6) in the X and Y directions, the marker 50 is moved alongwith the cell image on the viewscreen of the image display unit.

[0073] The fundamental concept of the present invention has beenexplained above. In addition, a method of successively attaching aplurality of markers to positions on the image of the specimen 7displayed on the viewscreen of the image display unit by a markerdisplay rule designated by an operator is explained below with referenceto FIGS. 7A and 7B. To begin with, as shown in FIG. 7A, the firstreference marker 51 is attached to the first reference position on theimage of the specimen 7. Next, as shown in FIG. 7B, the second referencemarker 52 is attached to the second reference position on the image soas to designate both the direction of a series of the successivelyattached markers and the pitch between two successive markers. By theabove method, a series of the successive markers 51, 52, and soon, canautomatically be attached to pertinent cell images of in the image ofthe specimen 7. Afterward, if the image of the specimen 7 is moved tothe left as shown in FIG. 7B, the markers 51 and 52 also move to theleft along with the positions to which the markers 51 and 52 areattached, and if the position to which the marker 53 is attached comesonto the viewscreen, the marker 53 is automatically displayed on thisposition.

[0074] Moreover, in this embodiment shown in FIGS. 7A and 7B, themarkers 51 and 52 are input and labeled with subindices of the numerals1 and 2, respectively. By inputting the subindices 1 and 2, markersafter the marker 52 are automatically labeled with numerals in anincreasing order. Conversely, if the markers 51 and 52 are input andlabeled with the numerals 2 and 1, respectively, all subsequent markersare labeled with numerals in a decreasing order. Also, the markers canbe labeled with a series of letters (for example, a, b, c, . . . ), orsubindices composed of alphanumeric pairs (for example, x1, X2, X3, . .. ). As mentioned above, by labeling the markers with subindices such asnumerals, since target cell to be observed in the specimen 7 can belocated with the help of the subindices, it becomes easier to search thetarget cell in the specimen 7.

[0075]FIG. 1 is a schematic diagram showing the composition of a chargerparticle beam irradiation apparatus using a scanning electronmicroscope, of an embodiment according to the present invention. Anelectron beam 2 emitted from an electron gun 1 is focused on thespecimen 7 by a convergence lens 6 and an objective lens 3. Also, thespecimen 7 is two-dimensionally scanned with the electron beam 2 byusing a deflection coil 5. Further, the secondary electrons emitted fromthe specimen 7 are detected and converted to image signals by asecondary electron detector 16, and the image signals are then amplifiedby an amplifier 17. Furthermore, the amplified image signals are sent toan image memory 18. The two-dimensional scan of the specimen 7 isperformed with sawtooth wave signals generated by a two-dimensionalscan-control circuit 15, and the amplitude of the sawtooth wave, towhich the magnification of the scanning electron microscope is inverselyproportional, is controlled by a command signal sent from amicroprocessor (MPU) 19. The sawtooth wave signals are converted tocurrent signals via a drive amplifier 14, and the converted currentsignals flow in the deflection coil 5. The image data of the specimen 7,which are stored in the image memory 18, are read out asynchronously tothe two-dimensional scan of the specimen 7, and are displayed on theimage display unit 22 as an image of the specimen 7. Also, an inputoperation for changing the magnification is performed via amagnification level control terminal 33.

[0076] The specimen 7 is mounted on the specimen stage 8, and thespecimen stage 8 can be two-dimensionally moved by the specimen stagedriving mechanism 10. The specimen stage driving mechanism 10 iscomposed of the specimen stage driving device 10X and the specimen stagedriving device 10Y which are driven by stepping motors 23X and 23Y,respectively. The stepping motors 23X and 23Y are further driven bydrive circuits 24X and 24Y based on drive pulse signals generated byspecimen stage movement-control circuits 25X and 25Y. Also, the specimenstage movement-control circuits 25X and 25Y detect the displacementquantities of the movement of the specimen stage 8 in the X and Ydirections carried out by the specimen stage driving devices 10X and 10Yby counting the number of the pulse signals sent to the drive circuits24X and 24Y. The input operation for moving the specimen 7 is carriedout by using a specimen movement-control terminal 31, and thedisplacement quantities in the X and Y directions, which are input bythis operation, are sent to the MPU 19. Further, the movement of thespecimen 7 is controlled based on command signals for designating thedisplacement quantities of the movement of the specimen 7 in the X and Ydirections, which are sent from the MPU 19 to the specimen stagemovement-control circuits 25X and 25Y. In addition, the deflection coil4 for moving the field of the viewscreen is provided to move the fieldof the viewscreen by moving the scan area of the specimen 7, which isscanned with an electron beam. This deflection coil 4 is controlled by afield movement-control circuit 13 via a drive amplifier 12.

[0077] In this embodiment, a pointing device 27 is used for designatingan optional position on the image displayed on the image display unit22. The display of a pointer such as an arrow mark, which is displayedon the viewscreen of the image display unit 22, is carried out based onpointer display signals generated by a pointer display circuit 9, andthe pointer display signals are superimposed on image display signals inan image addition circuit 11. Afterward, the superimposed signals aredisplayed on the image display unit 22. Also, the moving of the pointeris performed by decoding signals sent from the pointing device 27 with apointing device signal reading circuit 28, and sending signals fordesignating the position of the pointer to the pointer display circuit9. Moreover, numerals and/or letters for subindices of markers are inputwith a keyboard 29, and the input numerals and/or letters are furtherdecoded by a keyboard signal reading circuit 30. Furthermore, thecharged particle beam irradiation apparatus using the scanning electronmicroscope, according to the present invention, includes a markerdisplay circuit 20 for generating signals to display a marker attachedto a position on the image of the specimen 7 and an image additioncircuit 21 for superimposing the signals output from the marker displaycircuit 20 on the image signals of the specimen 7. All the abovecircuits are controlled by the MPU 19 via a bus 26, and calculationsnecessary for the operations of these circuits are executed by the MPU19.

[0078] In the following, processing performed by the above chargedparticle beam irradiation apparatus using the scanning electronmicroscope and operations for the above charged particle beamirradiation apparatus will be explained with reference to FIG. 8. FIG. 8is a flow chart showing the operations of the charged particle beamirradiation apparatus and the processing executed by the apparatus ofthe embodiment. To begin with, in step S11, the specimen 7 is moved byusing the specimen movement-control terminal 31. If the first referenceposition on the image of the specimen 7 appears on the viewscreen, instep S12, by using the pointing device 27, the pointer is moved to thefirst reference position to which a marker is attached. Afterward, instep S13, the position of the marker is designated by pressing a buttonon the pointing device 27. Further, the marker display circuit 20, whichhas received signals for designating the position of the marker,generates signals for displaying the marker, and these marker displaysignals are superimposed on image signals of the specimen 7 by the imageaddition circuit 21. Furthermore, the marker 51 which is a cross cursorin this embodiment is attached to the first reference position on theimage displayed on the viewscreen by displaying the superimposedsignals.

[0079] Subsequently, in step S14, a numeral as a subindex with which themarker 51 is labeled is input from the keyboard 29. In step S15, if theinput numeral is “1,” the marker display circuit 20 displays the marker51 with the subindex “1” attached to the side of this marker 51. Next,the second reference position is also designated to attach markers tosuccessive target positions to be observed. The second referenceposition on the image of the specimen 7 sometimes is not shown on theviewscreen along with the first reference position. If the secondreference position is not shown on the viewscreen along with the firstreference position, in step S16, the field of the display is shifted toanother field by operating the specimen stage driving mechanism 10. InFIG. 7A, for the simplicity of explanation, it is assumed that both thefirst and second reference positions exist on the same viewscreen, andthat the second one neighbors the first one. In step S17, the pointer ismoved to the second reference position by using the pointing device 27,and in step S19, the marker 52 is attached to the second referenceposition by pressing a button of the pointing device 27. At the sametime, in step S19, a subindex of a numeral with which the marker 52 islabeled is also input. In this example, a numeral “2” is input as thesubindex for the marker 52.

[0080] In step S20, when acknowledging the inputting of the subindex forthe marker 52, the MPU 19 sends the marker display circuit 20 aninstruction signal for displaying the numeral “2” on the side of themarker 52, and the marker display circuit 20 which has received theinstruction signal displays the subindex “2” on the side of the marker52. Further, in step S21, the MPU 19 calculates the direction and thepitch necessary to successively display markers on the other targetpositions, based on the calculated direction and pitch. Furthermore, instep S22, the MPU 19 automatically calculates the increment or decrementwidth in a series of subindices with which the markers to be attached tothe target positions are labeled by using the subindices of the numeralsinput for the markers 51 and 52. That is, the increment or decrementwidth in the series of the subindices is obtained based on thedifference between the two input numerals. Afterward, in step S23, theMPU 19 determines what scope in the images of the target cells to whichthe markers have been attached can be displayed in the present displayfield, and it successively displays the markers attached to the imagesin the determined scope.

[0081] Next, in step S24, if the specimen stage 8 is moved to observe animage of another target cell in the specimen 7, the MPU 19 calculatesthe displacement amount of the image of the specimen 7 based on thedetected amount of the movement of the specimen stage 8. Further, instep S25, it is determined whether or not a marker attached to each cellimage displayed in the renewed field of the viewscreen was beingdisplayed in the previous field of the viewscreen. If some of themarkers checked in step S25 were being displayed in the previous field,their present positions on the image of the specimen 7 are calculated instep S26. Furthermore, in step S27, it is determined whether or notthese present calculated positions exist inside the renewed field. Ifthese present calculated positions exist inside the renewed field, instep S28, data about these positions are sent to the marker displaycircuit 20, and the marker display circuit 20 displays the predeterminedmarkers on these positions. Otherwise, in step S29, the circuit 20 doesnot execute the processing of displaying markers on these positions, andthe process returns to step S24. Conversely, in step S25, if some of themarkers determined in step S25 were being displayed in the previousfield, in step S30, their present positions on the image of the specimenare also calculated. Furthermore, in step S31, it is determined whetheror not these calculated present positions exist inside the renewedfield. If these calculated present positions exist inside the renewedfield, in step S32, the predetermined markers are displayed on theseposition. Otherwise, in step S33, the process of displaying markers onthese positions is not executed, and the process returns to step S24.

[0082] As shown in the flow chart in FIG. 8, each marker which has beendesignated to a cell image can move along with the specimen 7. Moreover,when cell images other than the images at the first and second referencepositions to which the markers 51 and 52 are attached come onto theviewscreen, a series of markers 53, 54, . . . are successively displayedon their respective objective positions, and subindices of numeralsdesignated in an increasing or decreasing order are also displayed onthe sides of the respective markers as shown in FIG. 7B. In the exampleshown in FIGS. 7A and 7B, the markers 51 and 52 are displayed on thefirst and second reference positions of cell images adjacent to eachother, and the markers 51 and 52 are further labeled with subindices ofnumerals “1” and “2”. Accordingly, if a marker 53 is displayed on thecell image adjacent to the second reference position of the cell imageon which the marker 52 is displayed, the marker 53 is labeled with asubindex of the numeral “3.” As a matter of course, if the marker 52displayed on the second reference position of the cell image two cellimages away from the first reference position on which the marker 51with the subindex “1” is displayed is labeled with a subindex “4,” aseries of markers is displayed on cell images on the line connecting thefirst and second reference positions in every three cell images, and theseries of the respective markers is labeled with a series of subindices“1,” “4,” “7,” . . .

[0083] The scanning electron microscope in the charged particle beamirradiation apparatus shown in FIG. 1 includes the deflection coil 4 tomove the field of the viewscreen by shifting the scan area of thespecimen 7, which is scanned with an electron beam. The deflection coil4 is controlled by the field movement-control circuit 13 via the driveamplifier 12, according to instruction signals for the movement of thefield sent from the MPU 19, which has received operation signals inputfrom the irradiation area movement-control terminal 32. The amount ofthe movement of a cell image due to the movement of the irradiationposition is calculated based on the equations (5) by the MPU 19, andthis calculated amount of the movement of the cell image is sent to themarker display circuit 20. The whole process executed by the chargedparticle beam irradiation apparatus and operations of this apparatus formoving the field of the viewscreen by shifting the irradiation area issimilar to that of moving the field of the viewscreen by moving thespecimen 7. Therefore, explanation of this process is omitted. Also,according to this flow, a marker attached to each cell image on theimage of the specimen 7 moves along with the cell image, following themovement of the corresponding cell in the specimen 7, and if a cellimage which was outside the viewscreen comes onto the viewscreen, apredetermined marker is displayed on this cell image.

[0084] In the scanning electron microscope, its magnification is usuallyaltered by changing the scan area of the specimen 7, which is scannedwith an electron beam. In the following, a method of moving a markerattached to a cell image by changing the magnification will beexplained. FIG. 9 is a flow chart showing processing executed by thecharged particle beam irradiation apparatus when the magnification ofthe scanning electron microscope is increased. This flow chart is madeassuming that markers are already attached to images of target cells tobe observed.

[0085] Here, in the first step S41 of this flow chart, the changing ofthe magnification is carried out by using the magnification levelcontrol terminal 33.

[0086] The MPU 19, which has received the input operation signals forchanging the magnification, sends an instruction signal to change themagnification to the two-dimensional scan-control circuit 15, and thetwo-dimensional scan-control circuit 15 changes the magnification bychanging the amplitude of the electron beam scanning, which determinesthe scan area of the specimen 7. At the same time, in step S42, the MPU19 determines whether or not any marker has been displayed on theprevious viewscreen. If at least one marker has been displayed, in stepS43, a new display position for this marker is estimated as explainedregarding the flow chart shown in FIG. 8. Further, in step S44, it isdetermined whether or not the new display position of this marker existsinside the renewed field of the viewscreen. If the new display positionis inside the renewed field of the viewscreen, the MPU 19 sends the datafor this new position to the marker display circuit 20, and the circuit20 displays the predetermined marker on the new display position.Conversely, if the new display position of this marker goes outside thepresent viewscreen, in step S46, the process of displaying a marker isnot performed, and the process returns to step S41.

[0087] On the other hand, if any marker has not been displayed on theprevious viewscreen, new display positions of the predetermined markerswhich were already attached to the cell images are estimated again instep S47. Furthermore, in step S48, it is determined whether or not anyone of the new estimated new display positions of the markers have comeonto the renewed field of the viewscreen. If some of the estimated newposition have come onto the viewscreen, in step S49, the predeterminedmarker is displayed on the new position. Conversely, if any one of theestimated new positions has come onto the viewscreen, in step S50, theprocess of displaying a marker is not executed.

[0088] According to the above-explained flow charts shown in

[0089]FIG. 8 and FIG. 9, the markers successively attached to cellimages can be moved along with the specimen 7 or the change of themagnification. The process then returns to step S41.

[0090] In the above embodiment, to successively attach markers to cellimages, the second reference position is designated as the position of acell image next to the cell image of which the display position isdesignated as the first reference position. If the number of cell imagesexisting from the first one to the last one is known in advance, thefollowing method of successively attaching markers to those cell imagescan be used. FIGS. 10A-10C are illustrations for explaining this method.

[0091] First, the specimen 7 is moved so that the first referenceposition {circle over (1)} on the image of the specimen 7 comes onto theviewscreen of the image display unit 22 as shown in FIG, 10A. In thisstate, as shown in FIG. 10, the pointer is moved to this first referenceposition to which a marker is attached, and a marker 55 is attached tothis position. At the same time, a subindex(“1” in the example shown inFIG. 10B) is input, and the marker 55 is labeled with this subindex “1.”This process is the same as that in the above embodiments shown in FIGS.6A and 6B or FIGS. 7A and 7B. Afterward, the specimen 7 is further movedso that the second reference position {circle over (2)} on the image ofthe specimen 7 comes onto the viewscreen of the image display unit 22 asshown in FIG, 10A. Furthermore, as shown in FIG. 10C, the pointer ismoved to this second reference position to which a marker is attached,and a marker 56 is attached to this position. Also, a subindex(“20” inthis example shown in FIG. 10C) is input, and the marker 55 is labeledwith this subindex “20.”

[0092] The subindex “20” is the number of the final cell image, and thedifference between the number “20” of the final subindex and the number“1” of the first subindex indicates the division number of the intervalbetween the first and second (final) reference positions. Based on theinput subindices for the first and final reference positions, and thecoordinates of these positions, the MPU 19 estimates each position towhich a marker is attached between the first and final positions.Further, the MPU 19 sends the marker display circuit 20 an instructionsignal such that pairs of a marker and its subindex are displayed ononly some of the estimated positions on the viewscreen. After thedisplay of these markers and their subindices is completed, if thespecimen 7 is moved, or the magnification is changed, the displayedmarkers and their subindices can be moved along with the cell images towhich the markers are attached by the same processing as that carriedout in the aforementioned embodiments. By the above-mentioned method, aconvenient and efficient function for searching each of the cell imagesbetween the first and final positions can be realized.

[0093] In the above embodiments, a cross mark is used as a marker.However, another type of marker can be also used. FIGS. 11-13B showexamples of marker display of another embodiment. In the example shownin FIG. 11, a cross line is used as a marker, and the visibility of across line is excellent. Furthermore, a horizontal line or a verticalline alone can be also used as a marker, depending on the object ofobservation for the specimen 7. FIGS. 12A and 12B are examples of markerdisplay, in which either a vertical line marker or a horizontal linemarker is used, respectively. For the above marker display, theselection of either a vertical line marker or a horizontal line markeris input in advance from an input device such as the keyboard 9 so thateither a vertical line marker or a horizontal line marker alone isattached to the display positions on the image of each cell as shown inFIG. 12A or FIG. 12B. Also, it is possible to label each line markerwith a subindex as shown in FIG. 12A or FIG. 12B.

[0094] Moreover, if markers are successively displayed, as shown in FIG.13A, it is also possible to successively display each marker as a pairof lines perpendicularly intersecting each other on the cell images towhich markers should be attached. Furthermore, as explained for FIGS.12A and 12B, if one-line marker displaying is effective for the objectof observation for the specimen 7, lines of only one direction of crossline markers can be displayed. FIG. 13B shows an example in which onlyvertical lines of cross line markers are displayed as markers.

[0095] FIGS. 14A-14C are examples of marker display, in which theprocedure of successively displaying vertical line markers as shown inFIGS. 13A and 13B in one direction is used. To begin with, as shown inFIG. 14A, the first reference position 58 is designated in the samemanner as that in the above-mentioned embodiments. Next, the secondreference position 59 is also designated by moving the pointer to theposition 59. Subsequently, vertical line markers 71, 72, 73, and 74 aredisplayed perpendicular to the line connecting the positions 58 and 59on the viewscreen of the image display unit 22. Moreover, when thecompletion of the input operations is input from the keyboard 29, theMPU 19 determines that a line in the designated direction of eachcross-marker is to be attached to a corresponding position as a marker,and further displays line-markers perpendicular to the directionconnecting the positions 58 and 59 as shown in 14B. Furthermore, if thethird reference position 60 is designated as shown in FIG. 14C, linemarkers 76, 77, and 78 perpendicular to the already displayed linemarkers 71, 72, 73, and 74 are displayed with a pitch P shown in FIG.14C. By using the line markers shown in FIG. 11, FIGS. 12A and 12B, andFIGS. 13A and 13B, it is possible to deal with the image of the specimen7 as if graduations are drawn on the image. FIG. 15A and 15B show anexample of search for a cell image, which is performed by using markers,and in this example, by inputting the subindex of a numeral and/or aletter with which a marker attached to the target cell image to besearched is labeled, the target cell image designated by the inputsubindex for the marker can immediately be seen on the viewscreen. Also,it is assumed that the markers are labeled with subindices of numerals.

[0096] Now, in FIG. 15A, a cell neighboring a marker labeled with asubindex of “7” is being observed. As a matter of course, an operatorcan see only cell images displayed inside the field of the viewscreen 22a, and cannot see cell images other than these images. If the operatorintends to observe a cell image with a marker labeled with a subindex“8,” it is possible to locate this cell image by gradually moving thespecimen 7 with the specimen movement-control terminal 31 so that theimage of this cell comes inside the field 22 a of the viewscreen.However, in this embodiment, the subindex “8” with which the markerattached to this cell is labeled is input from the keyboard 29. When theMPU 19 receives an input signal for the subindex “8” the MPU 19estimates the distance between the positions in the presently observedcell images and the cell image to which the marker labeled with thesubindex “8” is attached. If the displacement amount of the cell image,which corresponds to this estimated distance, is within a range that canbe attained by a shift of the field of the viewscreen, performed by thedefection coil 4, then this displacement amount of the movement of thecell image is sent to the field movement-control circuit 13. Otherwise,this displacement amount of the image is sent to the specimen stagemovement-control circuits 25X and 25Y, and the field of the viewscreenis moved by this amount by moving the specimen stage 8. Thus, the nextcell image to be observed is brought onto the viewscreen.

[0097] In order to implement the above marker control, markers attachedto cell images are managed based on the coordinates of the positions ofthe cell images to which the markers are attached. Now, letting thecoordinates of the cell image to be presently observed and the cellimage to be next observed (X0, Y0) and (X8, Y8), respectively, thedisplacement amount of the field—that is, (X0-X8, Y0-Y8)—is sent to thefield movement-control circuit 13 or the specimen stage movement-controlcircuits 25X and 25Y if it is intended that the position of the cellimage whose coordinates are (X8, Y8) be shifted to the position (X0,Y0). Subsequently, the image display shown in FIG. 15B is quicklyobtained. The position (X8, Y8) is designated by inputting the subindex“8,” with which the marker attached to the cell image which ispositioned at (X8, Y8) is labeled, from the keyboard 29.

[0098] In accordance with the present invention, even if a large numberof cells are arranged in an orderly manner in the specimen 7, anoperator can easily search an image of a cell to be observed, byefficiently moving the field of the viewscreen, which greatly reducesthe operator's work of counting the number of cells and memorizingreference positions of cells and the numbers counted.

What is claimed is:
 1. A charged particle beam irradiation apparatuscomprising: a specimen stage for holding a specimen; a detector fordetecting the amount of said moved specimen stage; a charged particlebeam optical unit for irradiating said specimen with a charge particlebeam; an image display unit for displaying an image of said specimen anda marker on each target position on said image of said specimen, saidimage being formed by using charged particles or electromagnetic wavesemitted from said specimen irradiated with said charged particle beam;wherein, when said specimen stage is moved, said target position on saidimage of said specimen, on which each marker is to be displayed, is alsomoved based on both said target position of each marker, which has beencalculated, and the amount of said moved specimen stage, on said amountof displacement being detected by said detector.